Field of the Invention
This invention relates to chromatography, and concerns improved apparatus and techniques which in the disclosed embodiment of the invention are especially applicable to gas chromatography.
Chromatography is an analytical procedure wherein the components of a fluid mixture are physically separated to permit the individual component concentrations to be determined. In this procedure, a sample of the mixture is conducted by a carrier fluid through a column containing a material which retains the various mixture components for differing periods of time so that the components are separated to emerge at different times from the column. By providing a suitable detector at the output end of the column, measurement signals are developed responsive to component concentration. Such signals typically are used to develop a so-called chromatogram comprising a series of time-separated signal peaks each having a height corresponding to the concentration of a respective component.
Although chromatographic analyzers (or "chromatographs") originally were intended for use as laboratory instruments, there has been a continuing need to provide such equipment which can be used directly with industrial processes, particularly to enhance the control of such processes. The requirements applicable to such so-called process chromatographs are however quite different from those applicable to laboratory instruments. For example, process chromatographs generally will be operated under widely varying external conditions, and must be designed to be highly reliable as well as inherently safe in operation under such conditions. In addition, chomatographs for process control should be relatively inexpensive, and must provide for simple maintenance operations whenever required.
Field conditions for a process chromatograph may often include potentially explosive atmospheres such as found in a hydrocarbon distillation plant. Thus an exposed energy source, e.g. a flame or electrical device as used in certain laboratory chromatographs, cannot be employed in a process chromatograph without costly protective equipment or enclosures because such a device can cause a violent explosion resulting in the loss of equipment and even life. The present invention provides apparatus which effectively minimizes the danger of explosion, and particularly provides a process chromatograph which can be treated as inherently safe for use in potentially hazardous atmospheres.
Process control chromatographs generally should be capable of focussing on one or two components, so as to produce concentration signals respecting such components over a series of analysis cycles in order to obtain so-called "trend" information. In accordance with another aspect of the present invention, a process chromatograph is provided which includes unique means for identifying the peak representing a particular component of interest, and for generating a measurement signal respecting only that peak during each analysis cycle. An extension of this technique makes it possible to "track" more than one component if desired.